1. Field of the Invention
The present invention relates to a transmission electron microscope (TEM) capable of analyzing the three-dimensional structure of a specimen without sectioning it.
2. Description of Related Art
In the past, analysis of the three-dimensional structure of a specimen in TEM (transmission electron microscopy), i.e., three-dimensional reconstruction, has been performed by cutting ultrathin sections from the specimen and stacking TEM images of the sections. This procedure is also known as successive sectioning.
In this procedure, however, much labor is necessary to section a specimen. Furthermore, information about the height depends on the thickness of each section. Therefore, it has been difficult to obtain information providing a sufficient degree of quantitativeness and resolution because of thickness variations among the sections.
In recent years, attempts to reconstruct TEM images in three dimensions by making use of computerized tomography (CT) have been proposed. The CT method is a procedure consisting of reconstructing the internal distribution within an object from the principles of Radon and inverse Radon transforms. Its applications using X-rays in the medical field are well known.
If this CT method is applied to electron microscopy, a three-dimensional image containing information about the inside of a specimen can be reconstructed without sectioning it simply by obtaining TEM images in succession while varying the tilt angle of the specimen stage supporting the specimen. For example, Japanese Patent Laid-Open No. H4-337236 is known as a patent reference regarding an electron microscope for obtaining such three-dimensional images.
Where the CT method is applied to electron microscopy as mentioned previously, however, there are some problems intrinsic to electron microscopy, i.e., limitations on the tilt angle of the specimen stage and problems associated with identification of the axis of rotation and rotation and shift of the image.
For these reasons, the application of the CT method to electron microscopy has been limited to special cases.